Skip to content

Latest commit

 

History

History
159 lines (124 loc) · 3.57 KB

episode8.md

File metadata and controls

159 lines (124 loc) · 3.57 KB

app.init 方法的调用


从第四集我们发现,app.init 方法在 application.js 中定义。

// express/lib/application.js

app.init = function init() {
  this.cache = {};
  this.engines = {};
  this.settings = {};

  this.defaultConfiguration();
};

代码很容易了解,就是给 app 设置一些属性而已。

我们来重要的代码:

  this.defaultConfiguration();

defaultConfiguration 函数的定义:

app.defaultConfiguration = function defaultConfiguration() {
  var env = process.env.NODE_ENV || 'development';
  // default settings
  this.enable('x-powered-by');
  this.set('etag', 'weak');
  this.set('env', env);
  this.set('query parser', 'extended');
  this.set('subdomain offset', 2);
  this.set('trust proxy', false);

  // trust proxy inherit back-compat
  Object.defineProperty(this.settings, trustProxyDefaultSymbol, {
    configurable: true,
    value: true
  });

  debug('booting in %s mode', env);

  this.on('mount', function onmount(parent) {
    // inherit trust proxy
    if (this.settings[trustProxyDefaultSymbol] === true
      && typeof parent.settings['trust proxy fn'] === 'function') {
      delete this.settings['trust proxy'];
      delete this.settings['trust proxy fn'];
    }

    // inherit protos
    setPrototypeOf(this.request, parent.request)
    setPrototypeOf(this.response, parent.response)
    setPrototypeOf(this.engines, parent.engines)
    setPrototypeOf(this.settings, parent.settings)
  });

  // setup locals
  this.locals = Object.create(null);

  // top-most app is mounted at /
  this.mountpath = '/';

  // default locals
  this.locals.settings = this.settings;

  // default configuration
  this.set('view', View);
  this.set('views', resolve('views'));
  this.set('jsonp callback name', 'callback');

  if (env === 'production') {
    this.enable('view cache');
  }

  Object.defineProperty(this, 'router', {
    get: function() {
      throw new Error('\'app.router\' is deprecated!\nPlease see the 3.x to 4.x migration guide for details on how to update your app.');
    }
  });
};


defaultConfiguration 函数的分析: 涉及到的一些重要函数:

  1. enable
  2. set
  3. setPrototypeOf

我们一个个的来分析这些函数:

enable

app.enable = function enable(setting) {
  // 调用 set 方法, 第二个参数位 true.
  return this.set(setting, true);
};


set

app.set = function set(setting, val) {
  if (arguments.length === 1) {
    // app.get(setting)
    return this.settings[setting];
  }

  debug('set "%s" to %o', setting, val);

  // set value
  this.settings[setting] = val;

  // trigger matched settings
  switch (setting) {
    case 'etag':
      this.set('etag fn', compileETag(val));
      break;
    case 'query parser':
      this.set('query parser fn', compileQueryParser(val));
      break;
    case 'trust proxy':
      this.set('trust proxy fn', compileTrust(val));

      // trust proxy inherit back-compat
      Object.defineProperty(this.settings, trustProxyDefaultSymbol, {
        configurable: true,
        value: false
      });

      break;
  }

  return this;
};

我们发现set方法很简单,就是根据参数来判断进行不同的操作。

  1. 如果是一个参数,返回 app.settings[参数];
  2. 如果是两个参数,app.settings[第一个参数] = 第二个参数位


setPrototypeOf
这个函数就是给对象设置原型。


到目前,我们已经分析了 app 函数的定义
接下来,我们将分析 app 的属性。